Devices of the prior art for the quantitative analysis of biological, mineralogical, metallurigical samples, and the like, are specifically dedicated elaborate automatic instruments which utilize video scan cameras and various schemes to automatically interpret and display video signals. The two primary measurement parameters are size and density of cells within a sample. The more versatile of instruments of this class are exemplified by the device of U.S. Pat. No. 3,922,532, Kitchener, which provides a video monitor with manual controls whereby an operator may intervene to make judgments in cases of indefinite measurements. The primary advantage of these devices is their rapid automatic operation in evaluating large numbers of samples. This is of great importance in hospitals and research facilities where large numbers of specimens must be examined. In large facilities such as these the extremely high initial cost and ongoing maintenance expenses of such elaborate permanently installed devices are justifiable. However, small hospitals, clinics, and individual medical practitioners usually do not have access to, nor need of, such complex instruments. And the high purchase cost of these devices is prohibitive in economically depressed areas of the world, to small hospitals, and to individuals in private practice.
Furthermore, the devices of the prior art as exemplified by U.S. Pat. No. 3,922,532, Kitchener, and U.S. Pat. No. 2,731,202, Pike, do not discriminate among elements of a sample with the precision of a trained operator. Thus, with these devices, direct human intervention is often required. Recognizing this limitation, designers of the more sophisticated devices have provided means for identifying ambiguous measurements for subsequent operator evaluation. In light of the requirement of human intervention and judgment, a further disadvantage exists in that the human evaluator is required to examine a video display of the image of the sample. A video image is normally lower in resolution than is an original optical image formed by the microscope from which the video camera derives its electronically-produced image. Subtlety of texture and color in the specimen are distorted in video images, making such devices of limited use in many applications and entirely useless in others.
An example of current research in which the devices of the prior art would find little or no use is the work relating to the fruit fly. In this research it is necessary to discern minute variations in order to properly identify the eight known phenotypes of the insect. No fully automatic scanning device of the prior art could accomplish this task. The method used is laborious and is as follows: A quantity of fruit flies is distributed upon a slide and placed upon the stage of a dissecting microscope. While observing the sample by means of the microscope, a technician, with the aid of a tiny brush, physically separates the flies into individual piles, one for each phenotype. Afterwards, the technician counts the number of flies in each pile and records the number of each phenotype in the sample.
In the fields of material sciences and engineering there exist optical measuring intruments such as optical comparators, optical micrometers, and measuring microscopes. One class of these prior art devices is on the order of an illuminated projector which displays upon a frosted translucent screen a magnified silhouette of the object to be measured. In most such prior art devices, indexed knobs control the disposition of the object mounted on a movable stage relative to markings upon the face of the screen to bracket the image of the object to be measured. After such bracketing the operator interprets the knob settings as with conventional handheld micrometers to determine the value of the measurement. In optical projectors transparent overlay templates may be placed upon the translucent viewing screen. The templates bear one or a number of a variety of patterns to be used as a comparison to the sample under evaluation. For example, U.S. Pat. No. 4,054,782, Weibel, utilizes a variety of grid patterns in a device of this type.
Another and portable class of static optical measurment devices includes table-supported and handheld magnifying instruments featuring static reticles physically divided into grids, lines, and so forth, of precise dimensions. In this class are measuring microscopes and comparators. In some devices of this class an operator manually counts the number of grid elements required to span the sample, or, if the sample is smaller than a single grid element, the operator interpolates the percentage of the unit space spanned by the sample.
Other devices of this class for evaluating samples comprising a plurality of subjects such as biological cells provide a static array of a variety of population densities of the particular subject. Comparison of the array to the actual sample provides a rough approximation of the population density of the sample.
The primary disadvantage of these prior art devices is that the complex density of their static pattern often obscures the image of the sample, making accurate measurements difficult and confusing. The static display also requires the operator to manually count the number of measuring units spanned by the subject, an operation which is time consuming and prone to error.
The static use of a liquid crystal display (LCD) as a graticule of oscilloscopes is disclosed in U.S. Pat. No. 3,581,002, Dobbs, wherein a set of individually selectable static LCD graticules is provided to assist an operator in the evaluation of data displayed by a measuring oscilloscope. And U.S. Pat. No. 3,781,080, Aftergut, discloses the use of an LCD as a static reticle for optical equipment having two or more levels of magnification. In this invention each selectable static reticle pattern relates to a specific magnification level.